support multi-module (#4)

* add multimodule
* re-package modules

server/internal/router/middleware.go

@@ -0,0 +1,28 @@
+package router
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// LimitMiddleware limits number of concurrent connections using a buffered channel with limit spaces
+func LimitMiddleware(limit int) gin.HandlerFunc {
+	if limit <= 0 {
+		panic("limit must be greater than 0")
+	}
+	semaphore := make(chan bool, limit)
+	t := time.NewTimer(time.Millisecond * 100)
+
+	return func(c *gin.Context) {
+		t.Reset(time.Millisecond * 100)
+		select {
+		case semaphore <- true:
+			c.Next()
+			<-semaphore
+		case <-t.C:
+			c.Status(http.StatusGatewayTimeout)
+		}
+	}
+}